A Safety Probability Assessment at the Transportation-Planning Level: Should an Ordered or Unordered Response Be Used?

Abstract

In the context of urban network safety management, this article presents an alternative approach based on a qualitative response model, namely, the multinomial logit model. The main objective of this article is to compare and analyze the use of ordered and unordered mechanisms (such as the multinomial logit model) and consequently to select the appropriate model. To achieve this objective, urban segment data from Porto, Portugal, for a 5-year period were used. The ordered and the multinomial models were applied to estimate the parameters and marginal effects, considering three responses to reflect degrees of hazard (low, medium, and high). To compare and select the best model, statistical tests were conducted, and performance measures were obtained. Although similar results were obtained, the adjusted likelihood ratio test showed that the multinomial model was preferred. Moreover, to illustrate and compare a safety assessment using both models, the probability of each hazard level occurring was computed for two urban segments and hypothetical planned scenarios were defined. It was interesting to note that despite the slight apparent differences between the two models, great differences were found in the category probability model results, proving the importance of model structure selection. Â(c) 2013 Copyright Taylor and Francis Group, LLC.